if
Conditionally execute a group of commands.
Synopsis
if(<condition>)
<commands>
elseif(<condition>) # optional block, can be repeated
<commands>
else() # optional block
<commands>
endif()
Evaluates the condition argument of the if clause according to the
Condition syntax described below. If the result is true, then the
commands in the if block are executed.
Otherwise, optional elseif blocks are processed in the same way.
Finally, if no condition is true, commands in the optional else
block are executed.
Per legacy, the else() and endif() commands admit
an optional <condition> argument.
If used, it must be a verbatim
repeat of the argument of the opening
if command.
Condition Syntax
The following syntax applies to the condition argument of
the if, elseif and while() clauses.
Compound conditions are evaluated in the following order of precedence:
Innermost parentheses are evaluated first. Next come unary tests such
as EXISTS, COMMAND, and DEFINED. Then binary tests such as
EQUAL, LESS, LESS_EQUAL, GREATER, GREATER_EQUAL,
STREQUAL, STRLESS, STRLESS_EQUAL, STRGREATER,
STRGREATER_EQUAL, VERSION_EQUAL, VERSION_LESS,
VERSION_LESS_EQUAL, VERSION_GREATER, VERSION_GREATER_EQUAL,
and MATCHES. Then the boolean operators in the order NOT, AND,
and finally OR.
Possible conditions are:
- if(<constant>)
- True if the constant is 1, ON, YES, TRUE, Y,
or a non-zero number. False if the constant is 0, OFF,
NO, FALSE, N, IGNORE, NOTFOUND, the empty string,
or ends in the suffix -NOTFOUND. Named boolean constants are
case-insensitive. If the argument is not one of these specific
constants, it is treated as a variable or string and the following
signature is used.
- if(<variable|string>)
- True if given a variable that is defined to a value that is not a false
constant. False otherwise. (Note macro arguments are not variables.)
- if(NOT <condition>)
- True if the condition is not true.
- if(<cond1> AND <cond2>)
- True if both conditions would be considered true individually.
- if(<cond1> OR <cond2>)
- True if either condition would be considered true individually.
- if(COMMAND command-name)
- True if the given name is a command, macro or function that can be
invoked.
- if(POLICY policy-id)
- True if the given name is an existing policy (of the form CMP<NNNN>).
- if(TARGET target-name)
- True if the given name is an existing logical target name created
by a call to the add_executable(), add_library(),
or add_custom_target() command that has already been invoked
(in any directory).
- if(TEST test-name)
- True if the given name is an existing test name created by the
add_test() command.
- if(EXISTS path-to-file-or-directory)
- True if the named file or directory exists. Behavior is well-defined
only for full paths. Resolves symbolic links, i.e. if the named file or
directory is a symbolic link, returns true if the target of the
symbolic link exists.
- if(file1 IS_NEWER_THAN file2)
- True if file1 is newer than file2 or if one of the two files doesn’t
exist. Behavior is well-defined only for full paths. If the file
time stamps are exactly the same, an IS_NEWER_THAN comparison returns
true, so that any dependent build operations will occur in the event
of a tie. This includes the case of passing the same file name for
both file1 and file2.
- if(IS_DIRECTORY path-to-directory)
- True if the given name is a directory. Behavior is well-defined only
for full paths.
- if(IS_SYMLINK file-name)
- True if the given name is a symbolic link. Behavior is well-defined
only for full paths.
- if(IS_ABSOLUTE path)
- True if the given path is an absolute path.
- if(<variable|string> MATCHES regex)
- True if the given string or variable’s value matches the given regular
condition. See Regex Specification for regex format.
() groups are captured in CMAKE_MATCH_<n> variables.
- if(<variable|string> LESS <variable|string>)
- True if the given string or variable’s value is a valid number and less
than that on the right.
- if(<variable|string> GREATER <variable|string>)
- True if the given string or variable’s value is a valid number and greater
than that on the right.
- if(<variable|string> EQUAL <variable|string>)
- True if the given string or variable’s value is a valid number and equal
to that on the right.
- if(<variable|string> LESS_EQUAL <variable|string>)
- True if the given string or variable’s value is a valid number and less
than or equal to that on the right.
- if(<variable|string> GREATER_EQUAL <variable|string>)
- True if the given string or variable’s value is a valid number and greater
than or equal to that on the right.
- if(<variable|string> STRLESS <variable|string>)
- True if the given string or variable’s value is lexicographically less
than the string or variable on the right.
- if(<variable|string> STRGREATER <variable|string>)
- True if the given string or variable’s value is lexicographically greater
than the string or variable on the right.
- if(<variable|string> STREQUAL <variable|string>)
- True if the given string or variable’s value is lexicographically equal
to the string or variable on the right.
- if(<variable|string> STRLESS_EQUAL <variable|string>)
- True if the given string or variable’s value is lexicographically less
than or equal to the string or variable on the right.
- if(<variable|string> STRGREATER_EQUAL <variable|string>)
- True if the given string or variable’s value is lexicographically greater
than or equal to the string or variable on the right.
- if(<variable|string> VERSION_LESS <variable|string>)
- Component-wise integer version number comparison (version format is
major[.minor[.patch[.tweak]]], omitted components are treated as zero).
Any non-integer version component or non-integer trailing part of a version
component effectively truncates the string at that point.
- if(<variable|string> VERSION_GREATER <variable|string>)
- Component-wise integer version number comparison (version format is
major[.minor[.patch[.tweak]]], omitted components are treated as zero).
Any non-integer version component or non-integer trailing part of a version
component effectively truncates the string at that point.
- if(<variable|string> VERSION_EQUAL <variable|string>)
- Component-wise integer version number comparison (version format is
major[.minor[.patch[.tweak]]], omitted components are treated as zero).
Any non-integer version component or non-integer trailing part of a version
component effectively truncates the string at that point.
- if(<variable|string> VERSION_LESS_EQUAL <variable|string>)
- Component-wise integer version number comparison (version format is
major[.minor[.patch[.tweak]]], omitted components are treated as zero).
Any non-integer version component or non-integer trailing part of a version
component effectively truncates the string at that point.
- if(<variable|string> VERSION_GREATER_EQUAL <variable|string>)
- Component-wise integer version number comparison (version format is
major[.minor[.patch[.tweak]]], omitted components are treated as zero).
Any non-integer version component or non-integer trailing part of a version
component effectively truncates the string at that point.
- if(<variable|string> IN_LIST <variable>)
- True if the given element is contained in the named list variable.
- if(DEFINED <name>|CACHE{<name>}|ENV{<name>})
- True if a variable, cache variable or environment variable
with given <name> is defined. The value of the variable
does not matter. Note that macro arguments are not variables.
- if((condition) AND (condition OR (condition)))
- The conditions inside the parenthesis are evaluated first and then
the remaining condition is evaluated as in the previous examples.
Where there are nested parenthesis the innermost are evaluated as part
of evaluating the condition that contains them.
Variable Expansion
The if command was written very early in CMake’s history, predating
the ${} variable evaluation syntax, and for convenience evaluates
variables named by its arguments as shown in the above signatures.
Note that normal variable evaluation with ${} applies before the if
command even receives the arguments. Therefore code like
set(var1 OFF)
set(var2 "var1")
if(${var2})
appears to the if command as
and is evaluated according to the if(<variable>) case documented
above. The result is OFF which is false. However, if we remove the
${} from the example then the command sees
which is true because var2 is defined to var1 which is not a false
constant.
Automatic evaluation applies in the other cases whenever the
above-documented condition syntax accepts <variable|string>:
- The left hand argument to MATCHES is first checked to see if it is
a defined variable, if so the variable’s value is used, otherwise the
original value is used.
- If the left hand argument to MATCHES is missing it returns false
without error
- Both left and right hand arguments to LESS, GREATER, EQUAL,
LESS_EQUAL, and GREATER_EQUAL, are independently tested to see if
they are defined variables, if so their defined values are used otherwise
the original value is used.
- Both left and right hand arguments to STRLESS, STRGREATER,
STREQUAL, STRLESS_EQUAL, and STRGREATER_EQUAL are independently
tested to see if they are defined variables, if so their defined values are
used otherwise the original value is used.
- Both left and right hand arguments to VERSION_LESS,
VERSION_GREATER, VERSION_EQUAL, VERSION_LESS_EQUAL, and
VERSION_GREATER_EQUAL are independently tested to see if they are defined
variables, if so their defined values are used otherwise the original value
is used.
- The right hand argument to NOT is tested to see if it is a boolean
constant, if so the value is used, otherwise it is assumed to be a
variable and it is dereferenced.
- The left and right hand arguments to AND and OR are independently
tested to see if they are boolean constants, if so they are used as
such, otherwise they are assumed to be variables and are dereferenced.
To prevent ambiguity, potential variable or keyword names can be
specified in a Quoted Argument or a Bracket Argument.
A quoted or bracketed variable or keyword will be interpreted as a
string and not dereferenced or interpreted.
See policy CMP0054.
There is no automatic evaluation for environment or cache
Variable References. Their values must be referenced as
$ENV{<name>} or $CACHE{<name>} wherever the above-documented
condition syntax accepts <variable|string>.